Public utilities, such as municipal electricity companies and water and sewerage utilities, (or corresponding private utilities) manage large and complex systems. The maintenance of the systems must be arranged efficiently. A traditional way, for example in a municipal electricity company, is that maintenance groups, which belong to the company's staff, know their area, and before performing tasks they go to the office of the company to get task lists and, if needed, necessary map sheets. If some unexpected tasks occur during the working day, the maintenance groups may be informed and instructed by using a radiophone, mobile phone, normal telephone, or even a fax. It may also happen that new map sheets must be picked up from the office. The control center can be informed about operations made in the field using the same ways. Alternatively, the operations can be written down on paper and transported to the office or the control center after the tasks are completed.
Some public utilities may use mobile field computers, such as PDAs (Personal Digital Assistant), for informing maintenance men in the field. However, the field computers must also be updated in the office for the use of the day, before performing the tasks. A limited amount of instruction data may be delivered to the field computer via wireless communication, but larger data amounts are impossible (or very unpractical) to transport since the capacity of the wireless communication path is limited. After the tasks are performed, the field computers may be transported to the control center for updating the system in accordance with the operations made.
FIG. 1 illustrates, by way of a map, a simple example of an energy distribution network in an area. Watercourses are marked with horizontal hatched lines and larger consumption areas with diamond hatched lines. Main roads are also illustrated on the map. The power lines 4 are marked with dashed lines, switching stations 2 with circles, and supply transformers 3 with triangles. The generator 1 is marked with a circle with an amplitude current mark. It can be induced from the map that the distribution network comprises a great number of different elements with their attributes and parameters. For example, the energy distribution network of a city of about one million inhabitants may comprises 1.2-1.3 million targets (elements). The data amount, which is needed to describe a network of this size, is approximately over 100 Mbytes.
Nowadays, a trend is that public utilities externalize, for example, maintenance tasks. One company in the maintenance business may manage the maintenance of a very large area and/or of several areas, whereby the maintenance men do not any more know their areas and the networks. However, the maintenance men work the same way as before: they pick up their duties before starting to work and transport information about the operations made after the work. A problem is that the owner of the public utility (or corresponding private utility) may not desire to give all network information to the maintenance man of the external company. On the other hand, the external maintenance company may desire to use the same field devices, so it may happen that the device may contain information from several different utilities. The security of information is not as guaranteed as when the maintenance men were in the service of the utility. And as mentioned before, the huge amount of data of the systems is also a problem.
The goal of the invention is to alleviate the above-mentioned problems. This is achieved in a way described in the claims.